Commercial livestock raising operations continue to pursue ways in which output may be increased and costs per raised animal reduced. Recently, confined animal feeding operations (CAFOs) or "factory farms" have become widespread. These bear little resemblance to the animal husbandry operations of a century ago. In a confined animal facility, a single building houses thousands of animals, which may be cattle, pigs or poultry. In one commercial installation, about 38,000 animals are present in the facility at the same time.
The public has begun to object to these large-scale corporate farms as bad neighbors and water polluters. The keeping of thousands of animals means disposing of thousands of pounds of their bodily wastes, known as biodegradable mass or BOD (an acronym referring to the biological oxygen demand of the waste). There are two waste disposal methods which are presently employed in these operations.
The first is the spreading of untreated manure onto surrounding agricultural fields. While this fertilizes the field on which it is spread, this method produces quite objectionable odors during the spreading and creates water pollution from field runoff.
The second is the essentially anaerobic sewage treatment of the manure in large lagoons. This creates sludge disposal problems. The water used in treating the manure in this manner is released into the environment, but the water has large concentrations of ammonia and other nutrients which limit how often the wastewater can be applied to surrounding agricultural fields; only so much of the nutrients can be irrigated onto fields without exceeding the capacity of the plants therein to metabolize them. The loading of fields by wastewater streams typically is regulated by state environmental statutes. To the extent that these nutrients cannot be absorbed by the plants of the field on which they are put, the nutrients find their way into streams and rivers, creating environmental problems such as algal blooms and fish kills. There is also concern that these nutrients will begin to contaminate drinking water. Anaerobic lagoons also are remarkable for their odiferous emissions.
A combination aerobic and anaerobic lagoon has been developed by MFA Incorporated of Columbia, Mo. In this system, air is injected into the top six feet of the lagoon by diffusers which are suspended from the surface. Irrigation water and recycled water for the hog buildings to which this lagoon are connected are drawn out of the top eighteen inches of the lagoon. The MFA system is designed to control lagoon odor caused by H.sub.2 S. It still does not meet the need of reducing combined nitrogen nutrients in the treated lagoon water, will still result in the production of large quantities of sludge and, as such, points out the need for further improvements.